It is dirty, ageing, overcrowded and prone to breakdowns. But the London Underground has become one of the world's most expensive forms of transport, prompting a backlash by commuters.

The mayor of London, Ken Livingstone, is facing complaints about the fare increases of up to 25% which came into force this week.

A single ticket for a journey between any two stations in central London has risen from £1.60 to £2: two and a half times as expensive as in Tokyo, twice as much as in New York and 20 times higher than the standard fare in Moscow.

It costs more a mile than a cruise on the Queen Mary 2 or a first-class air fare to New York. It even exceeds the cost of the Heathrow Express, intensely criticised for charging £13 for the 15-minute journey from Paddington.

Rufus Barnes, the chairman of the statutory London Transport Users' Committee, said: "People won't understand why they have to pay more at a time like this. They're pretty hefty increases [given] the performance of a lot of central London transport."

The fares are a result of a behind-the-scenes budgetary battle which has left the mayor struggling for cash. Fearing the fury of voters in June's mayoral election, Mr Livingstone has sugared the pill by freezing prices for users of new pre-paid Oyster smartcards and limiting the rise on weekly and monthly Travelcards.

Transport for London pointed out that most tube travellers in central London used season tickets. But there are 170,000 adult single tickets sold in zone one every day.

Cynthia Hay of the Capital Transport Campaign said the price of a weekly zone one Travelcard had risen by 11% since Mr Livingstone was elected, despite his promise to keep fares pegged to inflation.

According to TfL's annual travel report the average fare had risen by a quarter in real terms over 11 years even before this week's hike.

Ms Hay said conditions on the network were unacceptable: "In the 90s, fares started going up on the basis that passengers should contribute to the modernisation of the underground," she said. "What have they got?"

Transport is the defining issue of Mr Livingstone's mayoralty. With a funding gap predicted to reach £1.1bn by 2006, he has little room for manoeuvre. The Treasury is reluctant to increase his government grant, considering him a profligate spender. The fares increase will raise £81m this year: a drop in the ocean in balancing the books.

A TfL spokesman said: "It all goes back to the fact that we get a certain amount in fare revenue and a certain amount in grant. The grant doesn't look like it's going to go up."

Bus users too are being asked to dig deeper. The flat bus fare in outer London has leapt from 70p to £1: a rise of 42%. Inner London fares have been frozen as part of a strategy to encourage people out of packed tubes and on to Mr Livingstone's 1,000 extra buses.

The increases will be a major election issue. Steve Norris, the Conservative mayoral candidate, does not dispute the need to raise ticket prices but he sees significance in the fact that Mr Livingstone appears to have reneged on cast-iron commitments made in his manifesto.

"What is remarkable about these price rises is not that they are happening but that Ken Livingstone said they wouldn't."

The mayor is making a number of political calculations. He took charge of the tube only last summer, and under the public-private partnership (PPP) he has limited control over the two private groups responsible for upgrading the infrastructure, Metronet and Tube Lines. This lets him raise prices on the tube and absolve himself of blame.

The calculation is different on the buses, which are the linchpin of his public transport policies. The number of people using buses is at its highest for 30 years. The buses, together with a shortfall in the proceeds of congestion charging, are largely responsible for the black hole in his transport finances and yet they retain a special status. Unlike money invested in the tube, money spent on buses quickly reaps discernible results. Buses have great ideological significance too, because poorer communities rely most heavily on them.

The prospect of a quick improvement on the underground is remote. Despite investment of £1.2bn during the first year of the PPP, the number of train failures rose by 23% and track problems by 20%.

New signalling systems and extra trains will eventually ease overcrowding by increasing the capacity by 23% but these improvements are due largely after 2012.

About 12,000 staff on 253 stations cope with 3 million tube travellers every day.

Cheaper ways to go

Single tickets are the most expensive way to travel in London. Here are the other options:

Oyster card

New electronic, blue plastic smartcards which cost £1.2bn to develop. Can be charged up with prepaid tickets, which have been frozen at 2003 prices. Can also be credited with a weekly, monthly or annual travelcard

Travelcard

Traditional season ticket providing free travel on buses, tubes and overground trains for a week, month or year. Usually the cheapest option

Carnet

Book of 10 single tickets for central London travel, priced at £15 instead of £20 - intended for visitors to the capital

Saver

Six bus tickets, priced at 70p each instead of £1

One-day Travelcard

Travel on buses, tubes and trains from 9.30am for £4.30 covering zones 1 and 2

One-day LT card

All-day travel on buses and tubes for £8.20 across the whole of Greater London